<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app"></div>
</body>
<script>
    const str='以后可以不睡觉吗'

    //js中写入html的方法
    document.querySelector('#app').innerHTML=str
</script>
</html>